Method for treating eluate from a chromatographic column



Aug. 26, 1969 c. SOCHOR METHOD FOR TREATING ELUATE FROM A CHROMATOGRAPHIC COLUMN Filed June 4. 1968 RECORDER p METER FIG. 2

l INJECTDR muscrolz esfmfi. jochar g INVENTOR.

United States Patent 3,463,615 METHOD FOR TREATING ELUATE FROM A CHROMATOGRAPHIC COLUMN Cestmir Sochor, Prague, Czechoslovakia, assignor to Ceskoslovenslra akademie ved, Prague, Czechoslovakia Continuation-impart of application Ser. No. 674,404, Oct. 11, 1967. This application June 4, 1968, Ser. No. 734,458 Claims priority, application Czechoslovakia, Oct. 13, 1966,

6,517/ 66 Int. Cl. G011! 31/08; B01d 19/00; G01j 1/00 US. Cl. 23-230 3 Claims ABSTRACT OF THE DISCLOSURE Reference to related application This application is a continuation-in-part of the co pending application, Ser. No. 674,404, filed Oct. 11, 1967 and now abandoned.

Background of the invention This invention relates to the analysis of liquids, and particularly to an improved method of preventing back-mixing of portions of the liquid while the liquid is being transferred to an evaluating station, and to improved apparatus for performing the method, as will be described hereinafter with specific reference to chromatography by way of example only.

It is often necessary to mix the eluate from a chromatographic column with a reagent to permit quantitative determination of the amounts of one or more components of the analyzed mixture. When the reaction is not instantaneous, the reagent is admixed to the eluate near the column, and the tubing which connects the column with the evaluating station is made long enough to permit the reaction to go to completion before the eluate enters the station. In order to avoid back-mixing of the several fractions of the eluate stream during the reaction, the diameter of the tubing is reduced as far as practical, to one millimeter or less, and the liquid in the normally capillary tubing is divided into sections by introducing small amounts of an inert gas into the eluate stream from time to time. It is normally necessary to remove the gas bubbles from the eluate prior to evaluation with which they would interfere.

This invention is more specifically concerned with the removal of the gas from the eluate stream. Some devices employed heretofore for eliminating the gas from the liquid eluate are relatively complex in that they require pumps. Others rely on relatively wide conduit sections following the capillary tubing in which the rate of flow is reduced and the gas is permitted to separate from the liquid by gravity. Some back-mixing cannot be avoided with the known arrangements. The sensitivity of many known arrangements is reduced because they require a portion of the liquid eluate to be discarded together with the gas bubbles.

The principal object of this invention is a method of removing gas bubbles from a stream of liquid in capillary tubing which does not affect the sensitivity of the analysis performed. A concomitant object is the provision of apparatus for performing the method which is simple and free from moving parts.

Summary of the invention We have found that the gas bubbles can be separated from the liquid by passing the liquid and the bubbles along an inner face of a wall which is impermeable to the liquid, but permeable to the gas, and by maintaining a pressure differential between the inner face and an outer face of the wall which causes the gas to pass through the wall at a rate sufiicient to remove the bubbles from the liquid before the liquid enters the evaluating station.

Many materials of construction satisfy the requirements outlined above, but two commercial fluorocarbon polymers, polytetrafluoroethylene and fluorinated ethylene propylene polymer, have been found to be permeable to gases having a low molecular weight, such as hydrogen and helium, at all pressures above 30 cm. water column in wall thicknesses practical and conventional in capillary tubing. The fluorocarbon polymers, moreover, are inert to and not wetted by the solvents normally employed as eluents in chromatography, and particularly aqueous eluents. The gas-permeable wall thus may constitute at least that terminal section of the capillary tubing between the chromatographic column and the evaluation station, which is near the station and remote from the column, as measured along the tubing.

Other features, additional objects, and many of the attendant advantages of this invention will readily be appreciated as the same becomes better understood by reference to the following detailed description of preferred embodiments when considered in connection with the attached drawings.

Brief description of the drawing In the drawing:

FIG. 1 shows chromatgraphic apparatus of the invention partly in elevational section, and partly in a diagrammatic manner; and

FIG. 2 illustrates a modification of the apparatus of FIG. 1 in a corresponding, but fragmentary view.

Description of the preferred embodiments Referring initially to FIG. 1, there is seen a container 1 provided with a loose cover 2 from which a coil 3 of polytetrafluoroethylene tubing is suspended. One end 4 of the coil is connected with an ion-exchange column 5, with an injector 6 attached to a bottle 7 of hydrogen gas under pressure, and with a reagent injector 8. The other end 9 of the coil 3 is connected to a photometer 10 equipped with a recorder 11.

The column 5 is filled with an ion exchange resin. The injector 6 may be of any type conventional in this art, as disclosed, for example in the Skeggs Patent No. 2,797,149 or the Ferrari Patents Nos. 3,072,442 and 3,074,784. The photometer 10 and recorder 11 also may be of any conventional type suitable for recording the transmissivity of a streaming liquid as a function of time.

The container 1 is normally filled with a heat transmitting fluid such as water or oil, and is kept at an elevated temperature maintained by a non-illustrated thermostat.

The apparatus illustrated may be employed for the conventional analysis of a protein hydrolysate in which the several amino acids sequentially eluted from an ion exchange resin (Arnberlite IR in the column 5 are reacted with ninhydrin admixed in solution by the injector 8. A pigment is formed by the slow interaction of ninhydrin with each amino acid, and the stream of liquid in the tubing 3 thus has alternating colored and colorless sections whose location is characteristic of the reacted amino acids under known process conditions.

To prevent back-mixing of the several liquid sections 12, hydrogen is injected into the eluate at regular intervals by the injector 6 to form bubbles 13.

Typically, the rate of eluate flow may be 30 ml. per hour, and ninhydrin solution may be added at a rate of 15 ml. per hour. At a temperature of 100 C. maintained by the liquid in the container 1, each colored reaction product of ninhydrin and amino acid is formed in about 20 minutes. The tubing 3 thus must have a capacity of 15 ml. of liquid plus a reserve for holding the gas bubbles 13. At an internal diameter of 1 mm., the length of the coil 3 must be more than 20 meters.

The column 5 and photometer are located above the container 1 at a height sufficient to maintain a minimum pressure differential of 30 cm. water column between the inner and outer faces of the tubing 3 whose wall thickness is about 0.1 mm. Under these conditions, the hydrogen gas can ditfuse outward through the plastic tubing at such a rate that the bubbles l3 disappear completely just ahead of the end 9 of the coil 2 so that they cannot interfere with the evaluation of the eluate in the photometer 10 in which the transmissivity of the eluate stream to light having a wavelength of 440 and 570 ,um. is measured whereupon the measurement is recorded on the recorder 11, as is conventional.

In the modification of the apparatus illustrated in FIG. 2, the coil employed in an otherwise unchanged apparatus has a first portion 14 of stainless steel which is connected to a second portion 15 of fluorinated ethylene propylene polymer by flanges 16. The dimensions of the coil and other conditions are balanced in such a manner that the gas bubbles which separate the several sections of an eluate in the steel tubing 14 are removed by diffusion through the polymer tubing 15 before the eluate is discharged from the coil.

The rate at which the inert gas of the bubbles 13 diffuses through permeable tubing depends on the nature of the tubing, the molecular weight of the gas, the prevailing temperature, the available pressure dilferential, and the dimensions of the wall in a manner well known in itself. Under otherwise fixed conditions, the diffusion rate can readily be controlled by adjusting the hydrostatic pressure in the tubing so that the bubbles disappear just ahead of the evaluating station, but not earlier. The pressure is most simply adjusted by raising or lowering the container 1 with the coil if the positions of the column 5 and of the photometer 10 are fixed.

A pressure differential of 1.5 atmospheres is to be maintained across the wall of the tubing portion 15 in FIG. 2 under conditions otherwise corresponding to those described with reference to FIG. 1 if the bubbles are to be removed over a -6 meter length of tubing having a thickness of 0.3 mm. and an internal diameter of 0.7 mm. Plastic tubing having a wall thickness up to 1 mm. has been used successfully.

Polymers which may replace the fluorocarbon materials specifically described above under suitable conditions include all commercially available fluorocarbon polymers. Sintered ceramic materials are useful over a more limited range of conditions, particularly when used wth eluents which do not wet the ceramic walls. They permit the use of nitrogen bubbles. Sintered aluminum oxide having a pore size of 50 microns has been used successfully with an aqueous eluate and nitrogen bubbles under a pressure of 750 millimeters Hg.

Polypropylene or florinated polypropylene are equally suitable for this purpose.

The invention has been described above with specific reference to an evaluating station in which an optical property of the reacted eluate is determined by a photometer, but the invention does not reside in the evaluating method employed, and its field of application is not limited to the specific method of eluate analysis described above. The ohmic resistance or any other electrical property of the several eluate sections may provide a quantitative indication of the amount of a specific component in the eluate, and it will be appreciated that electrical measuring methods also require the removal of an admixed gas in the manner described above.

Furthermore, the method and apparatus described above can readily be modified by those skilled in the art for application to methods of analysis not involving chromatography. Similar problems exist in routine blood and urine analyses, and the separation of gas bubbles from a liquid in such analyses remote from chromatography is specifically contemplated.

It should be understood, therefore, that the foregoing disclosure relates only to preferred embodiments of the invention, and that it is intended to cover all changes and modifications in the examples of the invention herein chosen for the purpose of the disclosure which do not constitute departures from the spirit and scope of the invention set forth in the appended claims.

I claim:

1. In a method of analysis in which a liquid is mixed with a reagent capable of forming a colored reaction product with a component of said liquid, the resulting mixture being liquid, the mixture is passed through elongated capillary tubing to an evaluating station for photometric evaluation, sequential sections of said mixture in the tubing are separated by bubbles of an inert gas, and the bubbles are removed before entry of said mixture into said station, the improvement which comprises:

(a) passing said sections and said bubbles through a portion of said tubing having a wall impermeable to said mixture, but permeable to said gas, said wall having respective faces in said tubing and outside said tubing;

(b) maintaining a pressure differential between said faces suflicient to cause said gas to pass outward of said portion of the tubing at a rate sufficient to 'remove the bubbles from said mixture before the entry of the same into said station,

(1) the rate of flow of said mixture in said tubing being low enough to permit completion of said reaction in said sections in said portion of the tubing while the gas of the bubbles separating said sections passes through said wall.

2. In a method as set forth of claim 1, said pressure differential being at least 30 cm. water column.

3. In a method as set forth in claim 1, said wall essentially consisting of polytetrafluoroethylene or fluori nated ethylene propylene polymer, said inert gas being hydrogen or helium, and said liquid being aqueous.

References Cited UNITED STATES PATENTS 2,911,057 11/1959 Green et a1 55-16 3,228,394 1/1966 Ayers 55-46 3,230,048 1/1966 Skeggs 23--253 3,246,449 4/1966 Stern et al. 55l6 3,246,450 4/1966 Stern et a1. 5516 3,347,096 10/1967 Person 5536 REUBEN FRIEDMAN, Primary Examiner CHARLES N. HART, Assistant Examiner US. Cl. X.R. 23253; 55-36 

